The present invention relates to a multispeed transmission for use in vehicles such as trucks. The transmission is particularly intended to provide a broad range of operating speed ratios while being designed to facilitate gear ratio changes within the transmission.
As will be made apparent in greater detail below, the transmission of the present invention is particularly contemplated as comprising a hydrodynamic torque converter providing a fluid coupling between a prime mover and a transmission speed ratio section.
The transmission speed ratio section may conventionally comprise a number of friction devices or brakes in order to establish a plurality of torque transmission paths therethrough. However, a preferred interconnection of the planetary gear sets within the transmission speed ratio section according to the invention is particularly intended to facilitate torque delivery through the transmission.
In addition, the invention is particularly directed toward a dual clutch assembly for selectively coupling an input shaft with various components in the transmission speed ratio section.
The prior art provides numerous illustrations of transmissions including a transmission speed ratio section generally of the type briefly described above. In view of the extensive prior art in this area, reference is particularly made only for purposes of example to U.S. Pat. Nos. 3,602,055; 3,678,784; 3,678,785; 3,653,118 and 3,705,521.
An additional specific feature of the present invention resides within a transmission of the type outlined above wherein a pair of input clutches may be engaged in unison to provide a selected intermediate gear ratio. Each of the two input clutches may then be separately engaged in combination with selected brakes or friction devices within the transmission speed ratio section to establish additional gear ratios either above or below the selected intermediate gear ratio.
A particular advantage realized from this combination resides in the design and operation of controls for both the input clutches and the friction devices within the transmission speed ratio section. Because of the arrangement described above, it is necessary only to disengage and reengage a single friction device in order to accomplish either an upshift of downshift between adjacent gear ratios within the transmission. This feature by itself is also contemplated in the prior art, for example noting the last patent cited above and also particularly noting U.S. Pat. No. 3,610,071. However, novel and advantageous operation of the present invention is achieved through design of the transmission wherein the two clutches are engaged in unison to establish an intermediate gear ratio. As will be apparent from the following description, this facilitates the design, construction and operation of a transmission having a broad range of operating speeds while particularly facilitating upshifting and downshifting between gear ratios.
In addition, the transmission of the present invention is designed to have a single friction device within the transmission speed ratio section engaged in order to establish a neutral condition within the transmission. The same friction device remains engaged in both first gear forward and first gear reverse. Initially, this feature facilitates shifting of the transmission in the same manner noted above since only a single friction device need be disengaged and a single friction device reengaged for an upshift or downshift between adjacent gears. Further, the single friction device within the transmission speed ratio section may be designed with sufficient torque capacity in order to accommodate torque converter stall in both first gear forward and reverse.
Additionally, as was also noted above, the present invention further contemplates a novel interconnection for a plurality of planetary gear sets within the transmission speed ratio section. The interconnection of these units is particularly intended to facilitate torque delivery through the transmission. Although this feature is intended for operation together with a dual input clutch assembly as described in greater detail below, it is also possible to employ the transmission speed ratio arrangement of the present invention in combination with other transmission input sections as well.
Additional advantages are realized within the present invention through the design of the transmission speed ratio section to provide a direct drive coupling between the transmission input and transmission output when the two input clutches are engaged in unison. The transmission speed ratio section is then capable of functioning in combination with engagement of one input clutch to provide relatively higher gear ratios (greater than 1.0) as suitable for low speed, high torque operation of the vehicle. The transmission speed ratio section is also adapted in combination with engagement with the other input clutch to establish a plurality of overdrive gears where the gear ratio is less then 1.0.
The dual input clutch assembly referred to above also comprises a particularly novel and useful portion of the present invention which may be used in a transmission of the type described above or in numerous other applications as well.